Conventionally, when a program for a cutting operation is created by an interactive mode, a cutting tool is sometimes required to carry out a plurality of cutting operations. For example, when a workpiece has a large target cutting amount, a cutting amount to be cut by a single cutting operation is designated in accordance with a type of cutting tool, a raw material of a workpiece, a cutting direction and the like, and the number of a cutting operations is designated by dividing a total cutting amount by the designated cutting amount.
In a conventional rough machining, however, since the number of cutting operations and a final cutting amount to be cut by a cutting tool are determined from a quotient and remainder obtained by dividing a target cutting amount by a designated cutting amount, the final cutting amount has various values ranging from zero to the designated cutting amount. When this final cutting amount has a very small value, it becomes very difficult to actually carry out a machining operation by using a rough cutting tool.
More specifically, since a cutting state and cutting tool life depend on a depth of a workpiece cut by a cutting blade in a cutting operation, a cutting amount must be designated to an optimum value in accordance with a configuration of a cutting tool, a material of a workpiece to be cut, a cutting speed and a feed. Therefore, an interactive type automatic programming unit generally has a standard cutting amount set therein as a parameter, and an operator arbitrarily changes this cutting amount within an effective cutting range, when necessary. Nevertheless, although a cutting amount must be set to an optimum value to increase the efficiency of a program and an actual machining efficiency, it is very difficult for the operator to manually change a final cutting amount to an optimum range.